1. Field of the Invention
This invention relates to a method making a SOI film having a more uniform thickness across the entire surface of a SOI substrate.
2. The Prior Art
Conventionally, as a method of forming a single crystal semiconductor thin film with a thickness of 1 micrometer or more on a dielectric substrate, the technique which comprises epitaxial growth of a single crystal silicon film and such on a single crystal saphire substrate has been well known. However, in this technique, because of the difference in the lattice constant between the dielectric substrate and the silicon single crystal which grows in the gas phase, many crystal defects occur in the silicon gas phase growth layer, rendering the practicality of said technique poor.
Because of this, joined wafers with a SOI (Si On Insulator) structure (hereafter referred to as SOI substrates) have been receiving attention lately. A SOI substrate is obtained by, for example: oxidizing at least one of two semiconductor substrates to form an oxide film on at least one of the two semiconductor substrates, stacking these two semiconductor substrates in such a way that said oxide film becomes the intermediate layer, bonding these by heating them up to a prescribed temperature, conducting surface grinding on one of the semiconductor substrates and further polishing it to make it a thin film, and thus obtaining a single crystal silicon thin film (hereafter referred to as a SOI film).